344 lines
12 KiB
Groff
344 lines
12 KiB
Groff
.TH CONTROLLER 4
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.SH NAME
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controller, disk, tape, at, bios, esdi, aha1540, ncr810, dosfile, fatfile \- controllers, disks and tapes
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.SH DESCRIPTION
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.de SP
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.if t .sp 0.4
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.if n .sp
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..
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The
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.BI c n *
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family of devices refer to drivers that control disks, disk like devices,
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and tapes. MINIX 3 contains a number of drivers for several different
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controllers. These controllers can have disks, cdroms and tapes attached to
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them. Boot Monitor variables specify which drivers are activated using
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the variables
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.BR c0 ,
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.BR c1 ,
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etc. The names of the devices in
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.BR /dev
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that correspond with the driver for controller 0 are all named beginning
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with
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.BR c0 .
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.PP
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For each controller, the minor device numbers are organized as follows:
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.PP
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.RS
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.nf
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.ta +\w'122-127nnmm'u +\w'd0p0s0nnmm'u +\w'disk 0, part 0, subpart 0nnmm'u
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.ft B
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minor device what? obsolete
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.ft P
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0 d0 disk 0 hd0
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1 d0p0 disk 0, partition 0 hd1
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2 d0p1 disk 0, partition 1 hd2
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3 d0p2 disk 0, partition 2 hd3
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4 d0p3 disk 0, partition 3 hd4
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5 d1 disk 1 hd5
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6 d1p0 disk 1, partition 0 hd6
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7 d1p1 disk 1, partition 1 hd7
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8 d1p2 disk 1, partition 2 hd8
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9 d1p3 disk 1, partition 3 hd9
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\&... ...
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39 d7p3 disk 7, partition 3 hd39
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.SP
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64 t0n tape 0, non-rewinding
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65 t0 tape 0, rewind on close
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66 t1n tape 1, non-rewinding
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67 t1 tape 1, rewind on close
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\&... ...
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78 t7n tape 7, non-rewinding
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79 t7 tape 7, rewind on close
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.SP
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120 r0 raw access device 0
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121 r1 raw access device 1
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\&... ...
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127 r7 raw access device 7
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.SP
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128 d0p0s0 disk 0, part 0, subpart 0 hd1a
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129 d0p0s1 disk 0, part 0, subpart 1 hd1b
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130 d0p0s2 disk 0, part 0, subpart 2 hd1c
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131 d0p0s3 disk 0, part 0, subpart 3 hd1d
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132 d0p1s0 disk 0, part 1, subpart 0 hd2a
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\&... ...
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144 d1p0s0 disk 1, part 0, subpart 0 hd6a
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\&... ...
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255 d7p3s3 disk 7, part 3, subpart 3 hd39d
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.fi
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.RE
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.PP
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The device names in
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.B /dev
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also name the controller, of course, so the usual place for the MINIX 3
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root device, the first subpartition of the second partition of disk 0 on
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controller 0 is
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.BR /dev/c0d0p1s0 .
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Note that everything is numbered from 0! The first controller is controller
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0, the first disk is disk 0, etc. So the second partition is
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.BR p1 .
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.PP
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The fourth column in the table above shows the disk devices names that were
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used by previous versions of MINIX 3 for what is now controller 0. These
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devices are no longer present in
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.BR /dev .
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.SS Disks
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Most disks are arrays of 512 byte sectors. The disk devices are normally
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block devices, which means they are block buffered by the MINIX 3 file system
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cache using 1024 byte blocks. The FS cache allows I/O at any byte offset,
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and takes care of cutting and pasting incomplete blocks together. If one
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creates a character device for a disk device, then I/O must be in multiples
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of the disk block size.
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.PP
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For each disk there is a device that covers the entire disk, these are named
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.BR c0d0 ,
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.BR c0d1 ,
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etc, up to
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.B c0d7
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for controller 0. If a partition table is placed in the first sector of the
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disk, then the disk is subdivided into regions named partitions. Up to four
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partitions may be defined, named
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.BR c0d0p0
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to
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.BR c0d0p3
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for disk 0 on controller 0. To make things interesting you can also place a
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partition table in the first sector of a MINIX 3 partition, which divides the
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partition into up to four subpartitions. Normally MINIX 3 is installed into a
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single partition, with the root, /home, and /usr file systems in subpartitions.
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.PP
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If a partition is an extended partition then it contains a linked list of
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partition tables each of which may specify a logical partition. Up to four
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of these logical partitions are presented by the driver as subpartitions of
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the extended partition.
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.PP
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A sector containing a partition table starts with 446 bytes of boot code,
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followed by four partition table entries of 16 bytes each, and ends with
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the magic number 0xAA55 (little endian, so first 0x55 then 0xAA.) Partition
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table information is defined in <ibm/partition.h>:
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.PP
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.nf
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.ta +2n +29n +37n
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/* Description of entry in the partition table. */
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struct part_entry {
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unsigned char bootind; /* boot indicator 0/ACTIVE_FLAG */
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unsigned char start_head; /* head value for first sector */
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unsigned char start_sec; /* sector value + high 2 cyl bits */
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unsigned char start_cyl; /* low 8 cylinder bits */
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unsigned char sysind; /* system indicator */
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unsigned char last_head; /* h/s/c for the last sector */
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unsigned char last_sec;
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unsigned char last_cyl;
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unsigned long lowsec; /* logical first sector */
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unsigned long size; /* size of partition in sectors */
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};
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.ta +24n +7n +37n
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#define ACTIVE_FLAG 0x80 /* value for active in bootind field */
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#define NR_PARTITIONS 4 /* number of entries in table */
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#define PART_TABLE_OFF 0x1BE /* offset of table in boot sector */
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/* Partition types (sysind). */
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#define NO_PART 0x00 /* unused entry */
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#define MINIX_PART 0x81 /* MINIX 3 partition type */
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.fi
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.PP
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The cylinder numbers are encoded in a very strange way, bits 8 and 9 are
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in the high two bits of the sector number. The sector numbers count from 1,
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not 0! More useful are the lowsec and size fields however, they simply give
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the location of the partition as an absolute sector offset and length within
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the drive.
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.PP
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The partition table entry defined above is specific to IBM type disks. The
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device drivers use another partition entry structure to pass information on
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a partition. This is what <minix/partition.h> looks like:
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.sp
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.nf
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.ta +2n +25n
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struct part_geom {
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u64_t base; /* byte offset to the partition start */
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u64_t size; /* number of bytes in the partition */
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unsigned cylinders; /* disk geometry for partitioning */
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unsigned heads;
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unsigned sectors;
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};
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.fi
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.PP
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The base and size fields are the byte offset and length of a partition.
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The geometry of the disk is also given for the benefit of
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partition table editors. This information can be obtained from an open disk
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device with the call:
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.sp
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.RS
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.ft B
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ioctl(\fIfd\fP, DIOCGETP, &\fIentry\fP);
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.ft R
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.RE
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.sp
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One can change the placement of the device to the lowsec and size fields of
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.I entry
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by using the
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.B DIOCSETP
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call instead. Only the base and size fields are used for
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.BR DIOCSETP .
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.PP
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The partition tables when read from disk by the driver are checked and
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truncated to fit within the primary partition or drive. The first sector
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is normally left free for the partition table.
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.PP
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The partition tables are read when the in-use count (opens and mounts)
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changes from 0 to 1. So an idle disk is automatically repartitioned on the
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next access. This means that DIOCSETP only has effect if the disk is in
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use.
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.SS "Disk-like devices"
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Devices like a CD-ROM are treated as read-only disks, and can be accessed
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using disk devices. A CD-ROM usually has a block size of 2048 bytes, but
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the driver knows this, and allows one to read at any byte offset by reading
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what isn't needed into a scratch buffer.
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.SS Tapes
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There are two kinds of tape devices: Non-rewinding, and rewind-on-close.
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The non-rewinding devices treat the tape as a series of files. The
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rewind-on-close devices look at the tape as a single file, and when you close
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such a device the tape is told to rewind.
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See
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.BR mt (1),
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and
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.BR mtio (4)
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for a description of the commands that may be sent to the tape, either from
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the command prompt or from a program.
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.PP
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There are two kinds of tape drives: Fixed and variable block size tape
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drives. Examples of the first kind are cartridge
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tapes, with a fixed 512 bytes block size. An Exabyte tape drive has a
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variable block size, with a minimum of 1 byte and a maximum of 245760 bytes
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(see the documentation of such devices.)
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The maximum is truncated to 32767 bytes for Minix-86 and 61440 bytes for
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Minix-vmd, because the driver can't move more bytes in a single request.
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.PP
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A read or write to a fixed block size tape must be a precise multiple of the
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block size, any other count gives results in an I/O error. A read from a
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variable block sized tape must be large enough to accept the block that is
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read, otherwise an I/O error will be returned. A write can be any size
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above the minimum, creating a block of that size. If the write count is
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larger than the maximum block size then more blocks are written until the
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count becomes zero. The last block must be larger than the minimum of
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course. (This minimum is often as small as 1 byte, as for the Exabyte.)
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.PP
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The
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.B mt blksize
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command may be used to select a fixed block size for a variable block sized
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tape. This will speed up I/O considerably for small block sizes. (Some
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systems can only use fixed mode and will write an Exabyte tape with 1024
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byte blocks, which read very slow in variable mode.)
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.PP
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A tape is a sequence of blocks and filemarks. A tape may be opened and
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blocks may be read from it upto a filemark, after that all further reads
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return 0. After the tape is closed and reopened one can read the blocks
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following the filemark if using a non-rewinding device. This makes the tape
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look like a sequence of files.
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.PP
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If a tape has been written to or opened in write-only mode, then a filemark
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is written if the tape is closed or if a space command is issued. No extra
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filemark is written if the drive is instructed to write filemarks.
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.SH DRIVERS
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By setting the Boot variables
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.BR c0
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to
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.BR c3
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under MINIX 3, or
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.BR c0
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to
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.BR c4
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under Minix-vmd one attaches a set of disk and tape devices to a driver.
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See
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.BR boot (8)
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for a list of boot variables that configure each of these drivers.
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The following drivers are available:
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.SS at
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The standard IBM/AT disk driver that also supports IDE disks. This is the
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default driver for controller 0 on AT class machines. (Most PCs are in that
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class.)
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.SS bios
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A disk driver that uses BIOS calls to do disk I/O. This is the default
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driver on anything but an AT. (Old XTs and PS/2s.) On an XT this is the
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best driver you can use, but on any other machine this driver may be
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somewhat slow, because the system has to switch out of protected mode to
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make a BIOS call. On a fast enough machine with a high enough setting of
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DMA_SECTORS (see
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.BR config (8))
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it works well enough.
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.SS esdi
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A hard disk driver for use on some PS/2 models.
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.SS "xt \fR(MINIX 3 only)"
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A hard disk driver for IBM/XT type hard disks. Useful for old 286 based
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machines that have such a disk. On XTs you are better off with the
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.B bios
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driver.
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.SS aha1540
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A SCSI driver for the Adaptec 1540 host adapter family, which includes the
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1540, 1540A, 1540B, 1540C, 1540CF, 1640, and 1740. Also supported is the
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compatible BusLogic 545.
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.SS ncr810
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This will eventually become a Symbios 810 SCSI driver. (Formerly owned by
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NCR.) KJB has read the docs on this card three times, but has still done
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nothing, the lazy bum.
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.SS dosfile
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The "DOS file as disk" driver that is used when MINIX 3 is running
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under DOS. It treats a large DOS file as a MINIX 3 disk. Only primary
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partitions are supported, there are no subpartitions. This is the default
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driver when MINIX 3 is started under DOS.
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.SS fatfile
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Uses a large file on a FAT file system as a disk. It needs one of the other
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disk drivers to do the actual I/O. This driver only knows how to interpret
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a FAT file system to find the file to use. With a fast native disk driver
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this driver is much faster than the
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.B dosfile
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driver.
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.SH FILES
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.TP 25
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/dev/c*d*
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Disks devices.
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.TP
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/dev/c*d*p*
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Partitions.
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.TP
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/dev/c*d*p*s*
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Subpartitions.
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.TP
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/dev/c*t*n, /dev/c*t*
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Tapes.
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.TP
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/dev/c*r*
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Raw access devices.
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.SH "SEE ALSO"
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.BR dd (1),
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.BR mt (1),
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.BR eject (1),
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.BR ioctl (2),
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.BR int64 (3),
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.BR mtio (4),
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.BR boot (8),
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.BR config (8),
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.BR monitor (8),
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.BR part (8),
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.BR repartition (8).
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.SH BUGS
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The subpartitioning is incompatible with the MS-DOS method of extended
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partitions. The latter does not map well to the sparse minor device number
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space.
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.PP
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The primary partition table is sorted by lowsec like MS-DOS does, subpartition
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tables are not. Just think about what happens when you delete a partition in
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the MS-DOS scheme.
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.PP
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Don't move a partition that is mounted or kept open by some process. The
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file system may write cached blocks to the new location.
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.PP
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The BIOS driver is not slow at all on a buffered disk.
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.PP
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Some IDE disks send an interrupt when they spin down under hardware power
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management. The driver acknowledges the interrupt as it is supposed to do by
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reading the status register. The disk then spins up again... You have to
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disable the spin down in the computer setup to fix the problem.
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.SH AUTHOR
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Kees J. Bot (kjb@cs.vu.nl)
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